The present invention relates to a fluid passage change over valve means, and more particularly to a valve means for use in a concrete pump having stationary double cylinders and pistons for intaking and discharging the concrete material alternatively.
Recently, crude concrete having low slump and including large gravel particular therein is used in civil engineering work. Such tendency will presumably increase in the future. In case of the employment of such kind of concrete material, it is necessary to reduce any resistive force exerted on discharge and intake passages, and switching of the flowing direction of the concrete should be easily made while reducing disadvantageous power or energy loss.
Conventionally, there has been a change-over-valve means for discharging crude concrete material, in which pistons are provided in double concrete cylinders, respectively, and alternatingly reciprocated therein, and simultaneously, intake and discharge ports are alternatingly opened and closed by flap valves disposed in the respective cylinders. However, such concrete pump may not perform excellent concrete intake and discharge properties, since the part to be sealed also functions as a fluid passage, and further, excellent durability may not be obtained.
Another type of concrete pump has been proposed in which double cylinders having a piston therein respectively are provided in a hopper, and a discharge pipe is pivotably provided to alternatingly communicate with the intake and discharge ports in response to the reciprocating movement of the piston. However, in such device, though intake and discharge properties may be improved, extremely large resistive force is subjected to the discharge pipe in switching operation of the pipe, particularly, in case of using a crude concrete having low slump and including large gravel, since extremely large power is required to shove aside the crude concrete material in order to move the pipe in the hopper. Further, total rigidity would become lowered because of the structure per se, which may reduce mechanical reliability.